Furnace



Dec. 10,- 1940. A. w. MACHLET FURNACE Filed Feb. 23, 1940 2 Sheets-Sheet l INVENTOR W h/aodz ATTORNEY Dec, 10, 1940. w, MACHLET 2,224,404

FURNACE Filed Feb. 23, 1940 2 Sheets-Sheet 2 FIG. 4

INVENTOR QI QQ ATTORNEY Patented Dec. 10, 1940 UNITED STATES PATENT oFFicE-T- 10 Claims.

The present invention relates to .an improved method and apparatus for use in the heat treatment of nonferrous and ferrous metals, particularly iron and steel and alloys thereof, and is concerned more particularly with .a furnace within which the atmosphere immediately surrounding the articles subjected to treatment may be carefully controlled. A primary aim of the invention is to render available a furnace capable of. general usage in which one has a definite control over the atmosphere in the immediate vicinity of the workpieces so that, for example, the ordinary hardening processes or case hardening processes employing nitriding or carburizing gases or mixtures thereof, brazing operations, or

annealing operations, may efficiently be carried out.

1 Still another object of the invention is to effect the heating of the workpieces in a manner ing in contact with the workpieces during the heating stage even though air may continuously be leaking into the furnace proper or when, in fact, the furnace door is wide open.

A further object of the invention is to effect substantial uniformity in heating and in the rate of heating of the workpieces or portions thereof in animproved manner and to effect such heating indirectly and while the workpieces themselves are completely isolated from the direct heat of the furnace and from the general atmosphere of the heating chamber.

A further aim of the invention is to enable the user to carry on simultaneously two or more like 35' or different heat treating processes within the same furnace, and to afford means whereby each process is capable of being separately controlled as to the temperature, time, and the work enveloping gas medium employed or, when desired, correlated with each other as to form sequential stages in the carrying out a single process.

Another aim of the invention is to increase the normal life period of the apparatus used'in heat treating processes and to render available a'furnace for such processes that will endure a long period of usage, is economical in heat units consumed, and is considerably less fatiguing to 0perate than the furnaces heretofore in use.

Still a further aim of the invention is to pro- 50 vide a furnace, adapted conveniently to handle flat work, dies, and plates, and the like, having a doorway for the entrance and removalxof workpieces that is considerably smaller in sectional area, and hence much smaller in air leakage 55; crevices, than has been possible heretofore. And

whereby the air is definitely prevented from cominvention it is proposed to construct a furnace with a heating chamber or oven about twice as high as is the conventional p'ractice, and to provide therein a relatively small doorway and to locate the door substantially in the lower half of the heating chamber. The entrance doorway is in height and sectional area approximately onethird the height and sectional area of the heating chamber.v

The furnace chamber may be heated by electricity, gas or oil in the conventional mannenfl and the workpieces to be treated, supported upon a hearth slab that is raised from the floor of the furnace a distance sufiicient to permit proper and substantially uniform distribution of heat thereunder and at thesame time to place the work receiving surface of the slab substantially level with the lower edge of the doorway.

With such a construction the available space provided within the oven chamber above 'the hearth slab will be approximately twice the vertical height of the doorway and in this space there is housed a vertically movable bell shaped retort or mufiie. The bell is closed on its four sides and top and is used completely to enclose, the workpieces that may be laid upon the hearth slab, and when placed in a work enclosing position, the bell may be effectively sealed around its edge against in-leakage of air, by means of fine sand or other suitable material. It is further proposed to charge the interior of the bell with such gases or gas mixtures as may be required for thelparticular type of heat treatment being carried out and to that end one or more gas ducts are connected to the bell and project to the exterior of the furnace for connection with the source of supply. In addition, the gas ducts are connected to a system of counterweighted levers so arranged that the operator may lift the bell off the hearth slab and into the upper portions of the oven chamber and thus permit convenient access to the workpieces without removing the hot bell from the furnace. By so arranging the bell as not to be removed from the furnace the; operator is not subjected to the heat thereof'in addition to the heat of theworkpieces, while handling the work outside of the furnace. Moreover, the bell itself is not subjected to rapid and life shortening changes in temperature.

In those instances when the nature of the work 5 to be heated requires two or more stages or periods of heating, or when it is desired to heat two batches of work simultaneously under like or difierent conditions, this invention proposes a furnace in which the furnace chamber is provided with a vertically extending partition wall which divides the chamber into two lateral compartments, each of which may be provided with a doorway similar to the doorway referred to above. With such a duplex construction, two

bells or retorts may be used, and the partition wall between compartments provided with a movable gate or door so as to permit access to, and the movement of work from, one compartment to the other without taking the work out of the furnace and exposing same to the external atmosphere.

This invention possesses the further advantages that a considerably smaller work entrance to the furnace may be provided because the atmosphere controlling retort is not to be removed from the furnace but stays inside of the furnace and ismerely raised or lowered therein. And the fact that the bell is always in the heating chamber and heat losses thereby reduced to their minimum, the furnace may be operated with a high degree of efficiency and economy. Moreover, when the bell is in a work enclosed position and the heating operation is being carried on, the furnace door may be leaking badly and in fact may be opened completely for burner or heating element inspection, flame color, etc. without producing any ill effects upon the workpieces.

A'further important feature of the invention 40 has to do with the excluding of air from contact with the work when the furnace door is opened, and also when the furnace door and the retort are both opened. Usually a furnace of this gen: eral character is provided with a flue for carrying off burnt combustion gases or spent treating gases, and in the present instance this stack is arranged automatically to be closed upon the opening of the furnace door. By closing the stack, and thus cutting out the flue action simultaneously upon the opening of the furnace door, the gases of combustion or the spent treating gases are necessarily forced out the doorway, and as the eiTective-opening of the door of the present furnace isrelatively small, the out-rush of 5; burnt or spent gases effectively prevents the entrance of air through the same door.

Usually the stack extends some distance above the height of the furnace door and tends to produce a reduced or negative pressure inside of the furnace proper when the door is closed, to the extent that external oxidizing air forces its Way. into the combustion chamber through the cracks about the doorway and other leakage crevices. To prevent the creation of such re- 5 duced pressure and resulting ingress of atmospheric air, this invention proposes to provide a second opening in the stack and to locate same at or about the level of the entrance door. During the normal operation of the furnace, the 70:.doorf level aperture in the stack is opened and any needed air is supplied therethrough. This door level opening functions, therefore, to produce a balance between the external and internal pressures, and when such a'balance pre- 75 vails there is no leakage of air. Under such conditions, the work enclosing bell may be raised and lowered within the heating chamber without danger of subjecting the hot workpieces to the action of an oxidizing or partially oxidizing atmosphere.

Other objects and advantages will be in part indicated in the following description and in part rendered apparent therefrom in connection with the annexed drawings.

To enable others skilled in the art so fully to 10 apprehend the underlying features hereof that they may embody the same in the various ways contemplated. by this invention, drawings depicting a preferred typical construction have been annexed as a part of this disclosure and, in such 15 drawings, like characters of reference denote corresponding parts throughout all the views, of which:

Figure 1 is a front elevational view of a furnace embodying the present invention. 20

Fig. 2 is a transverse sectional view thereof taken on a vertical plane.

Fig. 3 isa transverse sectional view taken on a horizontal plane at or about the level of the furnace door. 25

Fig.v 4 is a sectional view of a duplex furnace embodying the principles of this invention.

With respect to the embodiment of the invention represented in Figures 1-3, the furnace proper is of generally rectangular shape having 30 top, bottom and side walls I 0 constructed of suitable insulating refractory material encased by a steel sheath II. The legs l2, support the oven in spaced relation from the floor to permit convenient operation of the furnace and at the 3 same time to provide a space I2 for the heat supplying mechanisms (not shown in the drawings). Between the refractory walls III of the furnace and the outer sheathing, a space [3 is provided for additional insulating material 40 which further prevents objectionable radiation when the furnace is operated at high heat.

The interior of the present furnace is bounded by the bottom wall I 4, side walls [5 and an arched ceiling wall l6 which, in accordance with this 45 invention, is spaced a substantial distance from the floor and makes the furnace interior relatively high as compared with conventional ovens. Located midway in the front wall I0 of the heating chamber of the furnace, a small door- 50 way I! is provided which in height is approximately one-third the height of the heating chamber, and is so located in the front wall that the major portion is situated preferably in the lower half of the heating chamber. A vertically movable door l8 mounted in guides l9 and counterweighted by the mechanism indicated generally at 20, is provided for closing the opening l1.

One or two sets of burners 2| may be provided as desired to heat the furnace interior. However, inasmuch as the particular method of heating, whether it be oil, gas, or electricity, forms no part of the present invention, further description thereof is thought to be unnecessary. Suffice it to say that the spent gases of combustion or the spent treating gases are forced to the floor of the furnace and through openings 22 into a flue 23 which communicates with the vertical chimney 24. The chimney 24 extends preferably to the top of the furnace so that the attendant will not be burned by the outflow of hot gases. i

With such a construction, the height of the chimney tends to create a negative pressure within the heating chamber and thus promotes an in-leakage of air about the doorway, or other leakage points about the furnace, which is particularly objectionable in the heat treatment of workpieces which require at least a neutral atmosphere. By the present invention, however, that disadvantage does not exist, for a second duct is provided which communicates with the chimney 24 at a point approximately on the horizontal level of the doorway l'l. During the normal operation of the furnace, the duct 25 is opened to atmosphere and the hot gases of combustion or treatment thatmove in the chimney 24 and past the mouth of the duct, draw in such quantities of outside air as may be needed to maintain a substantial balance between the pressure within the furnace chamber and the external atmosphere. When there is no differential in pressures, there will not, of course, be any leakage of external air into the heating chamber.

In the present design of furnace the workpieces W are supported upon a hearth slab 26 of wear resisting heat conductive material, such as Sillimanite. The hearth in turn in supported upon Sillimanite blocks 21, in spaced relation with the floor I4 topermit a substantially uniform circulation and distribution of heat under the slab. In the present embodiment of the invention the hearth slab is provided with an upstanding marginal flange 28, the top of which is slightly above the lower margin 29 of the doorway l1 and as a slight step at this point would interfere with the sliding of workpieces in or out of the furnace, there is provided a supplemental sill 30 which brings the working surface of the hearth slab and the lower surface of the doorway in substantially coplanar relation.

The supplemental sill 30 is replaceable in character so that when it becomes worn and hollow by the abrading action of moving workpieces and tongs, a new sill may be inserted to restore the original coplanar relation.

The replaceable sill 30, as illustrated more clearly in Fig. 3, is formed with a row of indentations 3| along its leading edge of such size as not to defeat the function of the sill as a supporting platform, and yet large enough as to freely permit the distribution of heat around the front end of the hearth slab. A further purpose of the toothed sill is to permit spent gases that collect at the bottom of the furnace to be discharged through the doorway I! when the furnace door is opened.

To insure that such gases will be forced out of the doorway when the door is opened, the chimney 24, balancing duct 25 are automatically closed by covers 24 and 25 respectively, when the door I8 is elevated. The closing of the chimney 24 quickly generates a plus pressure in the heating chamber and the spent gases therein are forced out the doorway and inasmuch as the doorway of the present furnace is relatively small in proportion to the size of the heating chamber, the out-rush of burnt or spent gases efiectively prevents any inflow of air.

The automatic closing of the chimney 2 3 and duct 25 is effected by the lever mechanism 32 which is pivoted at 33 to the top of the furnace. The lever 32 extends forward and carries an adjustable screw 34 which is engaged by abutment 20* carried at the rear of the furnace door operating lever 20 When the lever 20 is rotated counterclockwise, as viewed in Fig. 1, the abutment 20 is lifted away from the screw 34 whereupon the lever 32 which operates the covers 24 and 25* moves clockwise by gravity (as viewed in Fig. 2) thereby closing the chimney 24 and balancing duct 25. When the main door I8 is lowered to its closed position, the lug 20* engages and rocks the lever 32 in the counter direction thus again opening the chimney and balancing duct.

To maintain the workpieces enclosed in a neutral atmosphere or in gases suitable for such treatments as nitriding or carburizing, or other heating processes, the invention proposes completely to enclose the work in a bell shaped retort 35 which is closed on its four sides and top. The retort overlays the workpieces as shown in Fig. 2 and preferably is sealed along its lower marginal edge with respect to the hearth slab by fine sand 36 or other suitable sealing material. To the top of the retort, two tubes 37 and 38 are rigidly secured which extend through the top wall of the furnace and are, in this exemplification of the invention, joined together by tubes 39 and Ml. The tubes 39 and 4d communicate with a common supply line 4i through which selected gases or gas mixtures may be conducted to the interior of the bell 35.

Lateral extensions 39 and W preferably nontubular in character, are secured to the rigid connections 31 and 38 and have a floating pivotal connection 62 with two arms 43 of a U- shaped elevating lever 44. The elevating lever is pivoted intermediate its ends at a point 45 and is weighted at its outer end by weights 46 which substantially counterbalance the weight of the parts carried at the opposite end including the bell retort 35. For convenience in operation, a connection 47 is made between the lever M and a foot treadle 48. When the lever M is operating in a bell raising direction, either by hand or by the foot treadle, the bell is lifted vertically away from the. hearth slab to the upper regions of the furnace thus allowing the operator free access to the work through the doorway ll. 1

The advantages of a vertically movable retort are many, among which may be noted that the operator may carefully control the atmosphere within the bell to suit the particular needs of the workpieces being treated and the character of the treatment desired without flooding the entire furnace interior with the treating gases. Moreover, the retort is never removed from the furnace as has been customary heretofore and is not, therefore, subjected to rapid changes in temperature and as a result the usable life of the retort is materially lengthened. And as it is now unnecessary to remove the retort from the furnace, the furnace doorway may be materially reduced in area with corresponding reductions in leakage areas.

The present invention also lends itself readily adaptable to the accurate measurement and control of the temperature that actually exists within the retort and to that end a thermocouple Q9 may be inserted into the bell through one of the conduits 37, 28 and used to indicate the temperature existing at the workpieces. Inasmuch as the workpieces are never subjected tothe direct heat of the heatingchamb-er but are heated indirectly through the walls of the retort and hearth slab on which they rest, the measuring of temperature within the retort affords the only certain way of determining the true heat of the workpieces being treated.

To operate the furnace the operator will place the workpieces upon the hearth slab and then lower the retort 35 thereover to the point at which it rests on the sand seal provided and close the furnace door l8. Meanwhile the gas or gas mixtures will have been flowing into the bell at a moderate rate, to exclude the air therefrom, and which continues to exclude air after it is placed in work closing position. Should the operator thereafter open the furnace door to inspect burner action, for example, or for any other reason, the workpieces remain fully covered and protected by the bell 35. Further protection of the work is afforded by the provision of the balancing duct 25 which as hereto-fore explained functions to keep the pressure within the heating chamber of the furnace substantially equal to that of the external atmosphere so that no objectionable inleakage of air can occur that would immediately attack the hot workpieces the moment the bell 35 was lifted. When, however, the door I8 is opened not only is the main chimney automatically closed but also the balancing duct, and a plus pressure is immediately generated within the heating chamber and the gases of combustion or spent treating gases force their way out the small doorway H and thus preventing ingress of oxidizing air. With such a condition prevailing, the bell 35 may then be elevated and the workpieces inspected, rearranged, etc. without danger of oxidization, and without removing either the bell or the workpieces from the furnace. When the workpieces have attained the required temperature, the bell is elevated and the work removed from the hearth slab and quenched or otherwise cooled by conventional methods. A new batch of work may then be inserted and as the bell has not lost any substantial heat, the expense of heating the new batch is materially reduced.

At the end of a heat treating operation the heating medium to the furnace is, of course, shut off. However, as the enclosed bell will retain substantial heat and cool slowly within the heating chamber, workpieces to be annealed may be inserted and covered by the bell and allowed to. stand until cold with a moderate gas pressure maintained therein to prevent scaling. In this way the retained heat of the bell'may completely and economically be put to beneficial use.

The duplex furnace represented by Fig. 4 preferably embodies in each compartment thereof all of the features and advantages heretofore mentioned in respect to the construction represented by Figs. 1 to 3, and need not, it is believed, be again discussed in detail. Sufiice it to say that each side of the duplex furnace may be operated independently of the other, or conjointly with each other in the carrying out of a given heat treating process.

In this modified form of the invention, a partition wall lil divides the furnace chamber into two substantially separate compartments, and a sliding gate IS, operable by a rod or a chain l8 or by mechanism of the order of the door raising mechanism 2t! previously referred to, is provided for the purpose of establishing communication between compartments to permit workpieces to be moved from one to the other without removing the work from the furnace proper. Such an arrangement is particularly advantageous when the workpieces are to be given an initial heating followed by a further heating at a higher temperature. In such a case both retorts 35 are elevated and the hot workpieces shifted from one chamber to the other while inside of the furnace and are not caused to come into direct contact with the external atmosphere. Moreover, the substantial independency of the two sides of the duplex furnace enables the operator to give precision like control to the temperature, to the duration of heat treatment, and to the. enveloping gas mediums used in either or both sides without interfering with the conditions existing in the other.

Without further analysis, the foregoing will so fully reveal the gist of this invention that others can, by applying current knowledge, readily adapt it for various utilizations by retaining one or more of the features that, from the standpoint of the prior art, fairly constitute essential characteristics of either the generic or specific aspects of this invention and, therefore, such adaptations should be, and are intended to be, comprehended within the meaning and range of equivalency of the following claims:

Having thus revealed this invention, I claim as new and desire to secure the following combinations and elements, or equivalents thereof, by Letters Patent of the United States:

1. A furnace for the heat treating of iron or steels or alloys thereof and non-ferrous metals and articles having a heating chamber defined by side walls, a bottom wall and a ceiling wall spaced a substantial distance from the bottom wall and means for heating said chamber, combining a hearth slab therein for supporting the Work to be treated, said slab having a marginal flange extending therearound, a bell shaped retort member permanently located within the heating chamber of the furnace adapted to rest upon said slab in covered relation with the work, means including said upstanding flange of the slab for effectively sealing the retort about its marginal edge against admission of gases from said chamber, and means operable from the exterior of the furnace for raising the retort vertically off said slab to permit access to the workpieces without removing the said retort from the heating chamber of the furnace.

2. A furnace for heat treating iron or steels or alloys thereof and non-ferrous metals and articles comprising a heating chamber defined in part by a bottom wall and a ceiling wall spaced a substantial distance from the bottom wall, a doorway in a lateral wall of said chamber, heating means for said chamber, a hearth slab in said chamber for supporting the work to be treated, a bell shaped retort member permanently located within the heating chamber of the furnace and adapted normally to rest upon said slab in covered relation with the Work and to enclose same, means for maintaining a controlled atmosphere within said retort separate from the atmosphere of the heating chamber, and means for raising the retort to the upper regions of the heating chamber to permit free access to the workpieces through said doorway.

3. A metal treating furnace having a heating chamber and a lateral doorway leading thereto, said chamber being defined in part by a bottom wall and a ceiling wall spaced a substantial distance from the bottom wall, the combination of a hearth slab in said chamber for supporting the work to be treated, a bell shaped retort member permanently located within the heating chamber of the furnace adapted normally to rest upon said slab in covered relation with the work for enclosing same, and a connection with said retort extending through an aperture in the furnace w'all other than the doorway to said chamber for raising the retort to the upper regions of the heating chamber thereby to permit access to the workpiece through the furnace doorway without removing the retort from the heating chamber.

4. The combination set forth in claim 3 characterized by the provision of means for excluding the atmosphere of the heating chamber of the furnace from the interior of said retort during a normal work heating period.

5. In a metal treating furnace having a heating chamber defined in part by a bottom wall and a ceiling wall spaced a substantial distance from the bottom wall, a doorway leading to said heating chamber, the combination of means in said chamber for supporting the work to be treated, a movable bell shaped retort member permanently located within the heating chamber of the furnace for enclosing the work to be treated and normally resting on said supporting means in covered relation with the work to be treated, and means extending through said ceiling of said chamber and operable from the exterior of the furnace for raising the retort oif said supporting means to the upper regions of the heating chamber to uncover and permit access to the workpieces through said doorway.

6. A furnace for heat treating iron or steels or alloys thereof comprising a heating chamber defined in part by a bottom wall and a ceiling wall spaced a substantial distance from the bottom wall, means for heating said chamber, a work support in said chamber, a vertically movable bell shaped retort member permanently located within the heating chamber of the furnace adapted normally to rest upon said work support in covered relation with the work, a furnace doorway leading to said chamber, said doorway having a cross-sectional area approximately onethird the cross-sectional area of said chamber, a vent for spent treating gases or gases of combustion communicating with said chamber, means for maintaining substantial equilibrium in the pressure inside of said heating chamber relative to the external air pressure during a normal work heating period; and means automatically operable to create a plus pressure within said chamber upon the opening of the furnace door whereupon said retort may be lifted off the work support for work inspection without danger of oxidation.

'7. A metal treating furnace having a work heating chamber and a chimney connected therewith for carrying off spent gases and in which said chimney tends to create a reduced pressure in said heating chamber, the combination of means for effecting a substantial balance between the pressure existing in said chamber and the pressure of the external atmosphere comprising an air duct communicating with the external atmosphere and with said chamber at a point intermediate said chamber and the chimney outlet, said duct being normally open during a work heating period serving to admit external air to the chimney in amounts sumcient to maintain, substantial balance between the pressure existing within the heating chamber and that of the external atmosphere throughout a normal work heating period. I

8. A furnace for use in the heat treatment of metal articles having a heating chamber relatively high in total altitude and a doorway in a lateral wall of thefurnace leading to said chamber whose cross-sectional area in. a vertical plane is approximately one-third the cross-sectional area of said chamber, and whose mean central axis is located below the mean central axis of said heating chamber, a chimney connected with said chamber at a pointbelow the level of said doorway for carrying off spent gases; and an air .duct communicating with said chimney for effecting substantial equalization in the pressure within said heating chamber relative to the external atmosphere during the normal period of heating the articles thereby to prevent an inleakage of air to said chamber, said point of communication of said air duct with the chimney being approximately 011 a level with said doorway where in-leakage normally is greatest.

9. A metal treating furnace having a heating chamber and a doorway leading to said chamber, said doorway having a sectional area in a vertical plane approximately one-third as large as the sectional area of said chamber and located substantially entirely in the lower portion of said chamber, a movable closure for said doorway, a chimney connected with the bottom of said chamber and extending to a point well above the level of the top of said doorway for carrying 01f spent gases, an air duct communicating with said chimney and the external atmosphere for affording an in-flow of air to the chimney to counteract the tendency of said chimney to create a pressure lower than atmospheric in the heating chamber, said air duct communicating with said chimney at or about the level of said doorway; and means automatically operable to close said chimney and said air duct upon the opening of the furnace doorway closure.

10. In combination with a metal treating furnace having a heating chamber and a work passageway leading thereto, a replaceable sill member for insertion in said passageway, said sill member being slightly longer than the length of said passageway so as to project into said heating chamber, and means along the said inner projecting edge of said sill member for permitting the flow of heatand gases vertically therethrough.

ADOLPH W. MACHLET. 

